1. Field of the Invention
The present invention relates to an image signal processing device, an imaging device, an image signal processing method and a program having a function of correcting so-called color mixture in a solid-state imaging device such as a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor) sensors using plural color filters.
2. Description of the Related Art
As arrangement of color filters of the imaging device, Bayer arrangement using two greens (G) Gr, Gb, one red (R) and one blue (B) in three primary colors which have good color reproducibility is known.
The Bayer arrangement is an arrangement in which resolution of luminance is regarded as more important than colors.
When a solid-state imaging device having plural light receiving elements on which color filters are formed is used in the solid-state imaging device, light is transmitted through adjacent light receiving elements due to factors such as incident angles and reflection of light after transmitting color filters.
As a result, so-called color mixture occurs, in which a signal value is obtained in a wavelength not in a transmission range of the color filters originally.
Incidentally, a pixel sharing system is commonly applied as a means for miniaturizing pixels.
The number of transistors per one pixel can be reduced by the system. For example, there is a zigzag type four-pixel sharing system (refer to S. Yoshihara, et al., “A 1/1.8-inch 6.4 MPixel 60 frames/s CMOS Image Sensor with Seamless Mode Change” ISSCC Dig. Tech. Papers, pp. 492-493, February, 2006 (Non-Patent Document 1)).
In the case of the sharing system, the same Gr pixel has two-types of layout structures. As the layout structure is different, the color mixture amount will be asymmetric.
The effect appears prominently in applications in which the incident angle is largely inclined to a vertical direction of a sensor surface such as in small modules used in a cellular phone application and so on. There is a need for a highly-accurate correction method which can correct asymmetric property of the color mixture amount along with miniaturization of pixels.
As one of methods of correcting of color mixture, a method in which mixture of a color to be corrected is reduced by multiplying each color of the color filters by a correction coefficient which is equal to all pixels and performs subtraction (refer to JP-A-56-147578 (Patent Document 1)).
Additionally, a method disclosed in JP-A-2005-278004 (Patent Document 2) is known as a correction method having coefficients different according to addresses.
In the method, correction of color mixture is performed by subtracting a value obtained by multiplying a signal value of a pixel adjacent to one side of a target pixel in the horizontal direction by a correction parameter unique to color temperature and an address from a signal value of the target pixel.
Operation expressions are represented by the following expressions and color mixture from the row direction can be corrected.R′(x,y)=R(x,y)−α(x,y)×Gr(x,y)B′(x,y)=B(x,y)−β(x,y)×Gb(x,y)Here, α(x,y)=R/Gr(x,y)−a(K)β(x,y)=B/Gb(x,y)−b(K)  [Expression 1]
*K represents color temperature